COYOTE CREEK WATERSHED HISTORICAL ECOLOGY STUDY Historical Condition, Landscape Change, and Restoration potential IN THE EASTERN SANTA CLARA VALLEY, CALIFORNIA UTIVE SUMMARY Prepared for the C Santa Clara Valley Water District By the San Francisco Estuary Institute EXE Courtesy Library of Congress, Geography and Map Division. Coyote Creek: 1869 Birdseye View This report synthesizes historical evidence into a picture of how Coyote Creek looked and functioned before intensive modification. This new view shows how the contemporary landscape was shaped and provides an array of tools for the restoration of watershed functions, natural flood protection, and integrated water management. studY OVERVIEW In recent years, a number of environmental research and management efforts in the Santa Clara Valley (“Valley”) have recognized the need for a better understanding of historical conditions as a basis for developing locally appropriate habitat goals and guidelines for restoration design. Understanding how habitat patterns and their controlling physical processes have been altered helps determine the relative potential for recovery, and suggests appropriate measures to implement. Fortunately, the Santa Clara Valley has a wealth of historical information which represents an untapped resource for understanding the origins and potential of today’s landscape. Historical OVERVIEW Coyote Creek’s naturally wide footprint has led to an unusual amount of publicly owned lands along the stream. This imposing morphology — including broad, flood-prone stream benches and long, dynamic braided reaches — tended to restrict streamside development. As a result, there is a relatively high proportion of city and county parkland that could contribute to stream health, through coordinated stream restoration and natural system-based flood protection activities. Additionally, EXecutive suMMarY contents while modified in many ways, Coyote // • Study and Historical Overviews E X E Creek has escaped major straightening. • Understanding Landscape Change Unlike most Bay Area streams, the C • Managing Watershed Functions and Processes UTIVE SUMMARY channel tends to follow its historical • Identifying Opportunities for Habitat Restoration route. These basic aspects of the stream’s • Developing Tools for Natural Flood Protection history contribute to significant present- day restoration potential. ES-1 COYOTE CREEK WATERSHED In this study, we mapped historical landscape patterns for the valley floor draining to Coyote Creek – an approximately 100-square-mile area on the eastern side of the Santa Clara Valley. This portion of Santa Clara County includes parts of the cities of San Jose, Milpitas, and Morgan Hill. The aerial photograph below shows the study area in 2002. A sampling of early images illustrates historical habitats mapped on the facing page. STUDY AREA H ISTORI Calera Creek C Tularcitos Creek A L Los Coches Creek Ec O L O G Y Berryessa Creek S T U D Y Lower Penitencia Creek Upper Penitencia Creek Coyote Creek Miguelita Creek Low gradient, perennial reach. South Babb Creek Lake Norwood Creek Cunningham Coyote Creek Evergreen Creek Narrow reach with perennial water and gravel bars. Thompson Creek Upper Silver Creek San Coyote Creek Francisco Fisher Creek Bay Broad, gravelly, Project Area intermittent Coyote stream bed. Coyote Watershed Fisher Creek 0 1 2 4 6 8 Miles Laguna Seca: 1:200,000 scale tules and ponds. ES-4 2002 Imagery Copyright 2005 AirPhotoUSA, LLC, All Rights Reserved ES-2 Before the modifications of the 19th and 20th centuries, the lands along Coyote Creek supported a remarkably diverse mosaic of habitats. Native grasslands and the celebrated valley oak savannas occupied the well-drained alluvial fans and natural levees along Coyote Creek. These areas (in yellow and orange on the map) became the most productive agricultural lands, primarily fruit orchards. CIRCA 1800 Lower-lying basin areas with clay soils supported mosaics of wetland habitats: wet meadows, ca. 1905 Calera Creek saltgrass-alkali meadows, willow groves, and perennial freshwa- ter wetlands, or lagunas. These Arroyo de los Coches areas, in green and blue, were difficult to farm and have been developed more slowly. Lower Penitencia Courtesy The Bancroft Library, UC Berkeley. UC Berkeley. Courtesy The Bancroft Library, Creek Upper Penitencia Creek 1896 South Babb Creek Laguna Socayre Coyote Creek Norwood Creek Courtesy History San José. Shallow Bay/Channel 1935 Tidal Flat Thompson Creek Upper Silver Creek Tidal Marshland with Channels and Pannes Coyote Creek Saltgrass-Alkali Meadow | Salitroso Tulare Hill Laguna Seca Wet Meadow Courtesy Cooper Ornithological Society. Courtesy Cooper Ornithological Society. Seasonal Lake | Laguna Seca and Perennial Freshwater Wetland | Tular Perennial Freshwater Pond | Laguna Coyote Creek 1916 Willow Grove | Sausal Fisher Creek // E X E Sycamore Grove | Alisal // C E X E Bars, Islands, and Inset Benches UTIVE SUMMARY Sycamore Alluvial Woodland and Riparian Scrub C UTIVE SUMMARY Valley Oak Savanna | Roblar 0 1 2 4 6 8 Courtesy the Santa Clara Valley Water District. Water Courtesy the Santa Clara Valley Miles Dry Grassland 1:200,000 scale Stream ES-7 ES-3 COYOTE CREEK WATERSHEDEXE C UTIVE SUMMARY ca. 1800 UNDERSTANDING LANDSCAPE CHANGE Many changes are easily overlooked, yet have significant present-day ramifications. DRAINAGE INTENSIFICATION Today nearly 50% of the valley floor water courses draining into Coyote Creek are constructed channels. These channels convey runoff across areas that previously had no surface drainage. The natural drainage network was highly discontinuous, H ISTORI supporting groundwater recharge on the coarse alluvial fans and wetlands in the valley bottomlands. C A L Before modification, most stream channels were Ec O L O G Y discontinuous…they spread out on the valley floor. S T U D Y The construction of drainage ditches and channels, which took place largely prior to 1900, has increased the density of drainage to Coyote Creek by about 40%. Further- unconfined groundwater basin more, the expansion of the underground storm drain network has resulted in nearly a tenfold increase in drainage density. Over 20 miles of artificial channel and 120 ca. 2006 miles of large, concrete storm drains now convey water from the unconfined groundwater zone that would otherwise contribute to recharge. Drainage density has increased dramatically… resulting in reduced infiltration and more rapid delivery of stormwater to Coyote Creek. unconfined groundwater basin RIPARIAN RECOVERY In this set of aerial photographs, riparian forest along Upper Penitencia Creek – heavily impacted by agriculture in the 1930s – has significantly expanded 1939 2002 with the creation of a protective land Imagery Copyright 2005 AirPhoto USA, LLC, All Rights Reserved. use buffer. Trajectories of change vary SPATIAL VARIABILITY While riparian forest has been lost along many creeks, a few substantially from reaches have shown notable improvement during the past place to place… few decades. Some streams have incised greatly, while others show almost no change over the past 150 years. We can look and there are some to these sites that have beneficial, positive trajectories as con- positive examples. temporary models for watershed protection and recovery. ES-4 Managing WATERSHED functions and processes Historical information provides a starting point for setting appropriate local goals. RIPARIAN HABITAT: ONE SIZE DOESN’T FIT ALL. While we tend to think of riparian habitat as a dense, closed canopy forest, this was not the dominant riparian type on Coyote Creek, where open savanna/woodland, riparian scrub, and large, unvegetated gravel bars were all important riparian components. Given that these habitat types have been disproportionately lost, watershed management efforts should consider their restoration at appropriate sites. SYcaMores and NigHTHawKS: interMittent is not necessarilY bad. Under natural conditions, most of Coyote Creek was seasonally dry (see center spread). The combination of intermittent reaches and perennial reaches (which were limited to the top and bottom of the valley), supported a wide range of native species, including the Lesser Nighthawk, which once nested in the gravelly creek beds but is no longer a breeding resident species. SYcaMore Alluvial Woodland: THE CHaracteristic Habitat of COYote CreeK Historical evidence indicates that Coyote Creek’s dominant riparian habitat was Sycamore alluvial woodland. Now mostly eliminated along the creek (and throughout the state), this habitat of episodic, gravel-dominated Central Coast streams had a relatively open tree canopy with widely-spaced sycamores — in contrast to the densely wooded contemporary conditions. Riparian conversion: Cottonwood forest replaces SYcaMore woodland Since the construction of Coyote Dam in 1936, peak flows from most of the upper watershed have been reduced, while summer flows have increased. As a result, trees have invaded the active channel, largely eliminat- ing unvegetated bars and open riparian habitat, and converting one riparian habitat type to another. While clearly possessing riparian value, these new habitats should probably be assessed for long-term viability and 1939 2002 Imagery Copyright 2005 AirPhoto USA, LLC, All Rights Reserved. ecological function. RiPARIAN HABITAT CONVERSION in the vicinity of Cottonwood Lake. “ …whose course COYote ValleY reacH: restoration is marked with and preservation opportunities. Some of the best existing examples of Coyote Creek’s